Lighting devices for transportation include automotive lamps, such as headlamps, that may comprise of light-emitting diodes as the source of illumination. The headlamps generally are used for driving and passing, which also refer to high beam and low beam of the vehicle. The source of illumination generates light which later is shaped properly for road illumination according to federal or government rules and regulations.
For low beams (passing beams), the rules and regulations generally define a cut-off of the illumination pattern at a certain vertical level. This cut-off helps to avoid glare for other drivers. There are various methods to create a cut-off depending on the type of the lamp and the light source used. For example, an intermediary baffle or shield may be used to create such a cut-off for low beam by blocking the passage of light.
The conventional methods of shaping illumination patterns for automotive lighting involve the use of elliptical or concave reflectors. It is known that these modules require complex and multi-step manufacturing processes. To emit sufficient light along the optical axis of the illumination pattern, elliptical reflectors must capture a majority of emitted light. To achieve this, reflectors must be considerably larger than the horizontally oriented source. A complex manufacturing process is used to mold the reflectors out of plastic material and then coat them with reflective materials such as aluminum.
A more recent method of shaping the illumination pattern comprises of using lightguides as a method of optical beam re-orienting. One example of such method is disclosed in U.S. Pat. No. 7,207,705 B2, where a lightguide is used along with multiple reflection surfaces to reorient the beam along the front optical axis. There are also headlamp designs based on lightguides with a method of cut-off formation. For example, a disclosure in U.S. Pat. No. 10,161,592 B2 implements a cut-off mechanism in which the cut-off pattern is controlled by horizontal edge faces within the body of the lightguide. The drawback of this design is that in order to generate a clear cut-off line, multiple modules must be used. In addition, the use of multiple modules contributes to processing time spent aligning the parts, as well as tighter tolerances for placing such elements, a larger size of overall component, and an increased risk for malfunction.
What is desirable is a single lightguide that forms the beam pattern using total internal reflections as well as forming the cut-off in a simpler way in order to avoid having multiple lightguides in a headlamp assembly or intermediary baffles.